Despite small workspace, parallel manipulators have some advantages over their serial counterparts in terms of higher speed, acceleration, rigidity, accuracy, manufacturing cost and payload. Accordingly, this type of ...Despite small workspace, parallel manipulators have some advantages over their serial counterparts in terms of higher speed, acceleration, rigidity, accuracy, manufacturing cost and payload. Accordingly, this type of manipulators can be used in many applications such as in high-speed machine tools, tuning machine for feeding, sensitive cutting, assembly and packaging. This paper presents a special type of planar parallel manipulator with three degrees of freedom. It is constructed as a variable geometry truss generally known planar Stewart platform. The reachable and orientation workspaces are obtained for this manipulator. The inverse kinematic analysis is solved for the trajectory tracking according to the redundancy and joint limit avoidance. Then, the dynamics model of the manipulator is established by using Virtual Work method. The simulations are performed to follow the given planar trajectories by using the dynamic equations of the variable geometry truss manipulator and computed force control method. In computed force control method, the feedback gain matrices for PD control are tuned with fixed matrices by trail end error and variable ones by means of optimization with genetic algorithm.展开更多
Traditional simulation methods are unable to meet the requirements of lunar takeo simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have th...Traditional simulation methods are unable to meet the requirements of lunar takeo simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have the advantages of high payload to weight ratio, potentially large workspace, and high-speed motion, these mechanisms have the potential to be used for lunar takeo simulations. Thus, this paper presents a parallel mechanism driven by nine cables. The purpose of this study is to optimize the dimensions of the cable-driven parallel mechanism to meet dynamic workspace requirements under cable tension constraints. The dynamic workspace requirements are derived from the kinematical function requests of the lunar takeo simulation equipment. Experimental design and response surface methods are adopted for building the surrogate mathematical model linking the optimal variables and the optimization indices. A set of dimensional parameters are determined by analyzing the surrogate mathematical model. The volume of the dynamic workspace increased by 46% after optimization. Besides, a force control method is proposed for calculating output vector and sinusoidal forces. A force control loop is introduced into the traditional position control loop to adjust the cable force precisely, while controlling the cable length. The e ectiveness of the proposed control method is verified through experiments. A 5% vector output accuracy and 12 Hz undulation force output can be realized. This paper proposes a cable-driven parallel mechanism which can be used for lunar takeo simulation.展开更多
A simple robust scheme of parallel force/position control is proposed in this paper to deal with two problems for non-planar constraint surface and nonlinear mechanical feature of environment： i） uncertainties in en...A simple robust scheme of parallel force/position control is proposed in this paper to deal with two problems for non-planar constraint surface and nonlinear mechanical feature of environment： i） uncertainties in environment that are usually not available or difficult to be determined in most practical situations; ii） stability problem or/and integrator windup due to the integration of force error in the force dominance rule in parallel force/position control. It shows that this robust scheme is a good alternative for anti-windup. In the presence of environment uncertainties, global asymptotic stability of the resulting closed-loop system is guaranteed; it environment with complex characteristics. Finally, numerical robot manipulator. also shows robustness of the proposed controller to uncertain simulation verifies results via contact task of a two rigid-links展开更多
The application of μ theory in compliant force control system is studied. A compliant force control strategy is developed based on the inner loop position control of 6-DOF parallel robot in order to simulate the push...The application of μ theory in compliant force control system is studied. A compliant force control strategy is developed based on the inner loop position control of 6-DOF parallel robot in order to simulate the push and pull process of forcible alignment in space docking, Considering uncertainties such as parameter perturbations, model perturbations and external disturbances, etc., a robust force controller is designed using μ synthesis theory. The robust stability and robust performance are compared by analysis between the designed robust force controller and the classical force controller. The experiment results of the designed robust force controller and the classical force controller are shown. The results indicate that the designed robust force controller is of efficiency and superiority.展开更多
The return capsule needs to be launched to the moon and return back to earth in the third stage of the Chinese lunar exploration project.Therefore,it is necessary to perform simulations on the ground.This paper presen...The return capsule needs to be launched to the moon and return back to earth in the third stage of the Chinese lunar exploration project.Therefore,it is necessary to perform simulations on the ground.This paper presents an 8-cable-driven parallel manipulator to achieve end-force output in a low-gravity environment.End-force output refers to the vector sum of the external force on the end-effector.A model of end-force output is established based on a kinematics model,a dynamic model,and a force analysis of an 8-cable driven parallel manipulator.To obtain end-force output in a low-gravity environment,the cable force has to be controlled to counteract gravity.In addition,a force-position mix control strategy is proposed to proactively control the cable force according to the force optimal distribution given by the closed-form force distribution method.Furthermore,a suitable choice for an end-force output is obtained by modeling the effect of cable force on end-force output.Experimental results show that the actual cable force agrees well with the calculated force distribution,indicating that it is feasible to realize end-force output in a low gravity environment.展开更多
This study proposed a force and shape collaborative control method that combined method of influence coefficients(MIC)and the elitist nondominated sorting genetic algorithm(NSGA-II)to reduce the shape deviation caused...This study proposed a force and shape collaborative control method that combined method of influence coefficients(MIC)and the elitist nondominated sorting genetic algorithm(NSGA-II)to reduce the shape deviation caused by manufacturing errors,gravity deformation,and fixturing errors and improve the shape accuracy of the assembled large composite fuselage panel.This study used a multi-point flexible assembly system driven by hexapod parallel robots.The proposed method simultaneously considers the shape deviation and assembly load of the panel.First,a multi-point flexible assembly system driven by hexapod parallel robots was introduced,with the relevant variables defined in the control process.In addition,the corresponding mathematical model was constructed.Subsequently,MIC was used to establish the prediction models between the displacements of actuators and displacements of panel shape control points,deformation loads applied by the actuators.Following the modeling,the shape deviation of the panel and the assembly load were used as the optimization objectives,and the displacements of actuators were optimized using NSGA-II.Finally,a typical composite fuselage panel case study was considered to demonstrate the effectiveness of the proposed method.展开更多
文摘Despite small workspace, parallel manipulators have some advantages over their serial counterparts in terms of higher speed, acceleration, rigidity, accuracy, manufacturing cost and payload. Accordingly, this type of manipulators can be used in many applications such as in high-speed machine tools, tuning machine for feeding, sensitive cutting, assembly and packaging. This paper presents a special type of planar parallel manipulator with three degrees of freedom. It is constructed as a variable geometry truss generally known planar Stewart platform. The reachable and orientation workspaces are obtained for this manipulator. The inverse kinematic analysis is solved for the trajectory tracking according to the redundancy and joint limit avoidance. Then, the dynamics model of the manipulator is established by using Virtual Work method. The simulations are performed to follow the given planar trajectories by using the dynamic equations of the variable geometry truss manipulator and computed force control method. In computed force control method, the feedback gain matrices for PD control are tuned with fixed matrices by trail end error and variable ones by means of optimization with genetic algorithm.
基金Supported by National Natural Science Foundation of China(Grant No.51405024)
文摘Traditional simulation methods are unable to meet the requirements of lunar takeo simulations, such as high force output precision, low cost, and repeated use. Considering that cable-driven parallel mechanisms have the advantages of high payload to weight ratio, potentially large workspace, and high-speed motion, these mechanisms have the potential to be used for lunar takeo simulations. Thus, this paper presents a parallel mechanism driven by nine cables. The purpose of this study is to optimize the dimensions of the cable-driven parallel mechanism to meet dynamic workspace requirements under cable tension constraints. The dynamic workspace requirements are derived from the kinematical function requests of the lunar takeo simulation equipment. Experimental design and response surface methods are adopted for building the surrogate mathematical model linking the optimal variables and the optimization indices. A set of dimensional parameters are determined by analyzing the surrogate mathematical model. The volume of the dynamic workspace increased by 46% after optimization. Besides, a force control method is proposed for calculating output vector and sinusoidal forces. A force control loop is introduced into the traditional position control loop to adjust the cable force precisely, while controlling the cable length. The e ectiveness of the proposed control method is verified through experiments. A 5% vector output accuracy and 12 Hz undulation force output can be realized. This paper proposes a cable-driven parallel mechanism which can be used for lunar takeo simulation.
文摘A simple robust scheme of parallel force/position control is proposed in this paper to deal with two problems for non-planar constraint surface and nonlinear mechanical feature of environment： i） uncertainties in environment that are usually not available or difficult to be determined in most practical situations; ii） stability problem or/and integrator windup due to the integration of force error in the force dominance rule in parallel force/position control. It shows that this robust scheme is a good alternative for anti-windup. In the presence of environment uncertainties, global asymptotic stability of the resulting closed-loop system is guaranteed; it environment with complex characteristics. Finally, numerical robot manipulator. also shows robustness of the proposed controller to uncertain simulation verifies results via contact task of a two rigid-links
文摘The application of μ theory in compliant force control system is studied. A compliant force control strategy is developed based on the inner loop position control of 6-DOF parallel robot in order to simulate the push and pull process of forcible alignment in space docking, Considering uncertainties such as parameter perturbations, model perturbations and external disturbances, etc., a robust force controller is designed using μ synthesis theory. The robust stability and robust performance are compared by analysis between the designed robust force controller and the classical force controller. The experiment results of the designed robust force controller and the classical force controller are shown. The results indicate that the designed robust force controller is of efficiency and superiority.
基金This research was supported by National Natural Science Foundation of China(No.91648107)Beijing Natural Science Foundation(No.L182041).
文摘The return capsule needs to be launched to the moon and return back to earth in the third stage of the Chinese lunar exploration project.Therefore,it is necessary to perform simulations on the ground.This paper presents an 8-cable-driven parallel manipulator to achieve end-force output in a low-gravity environment.End-force output refers to the vector sum of the external force on the end-effector.A model of end-force output is established based on a kinematics model,a dynamic model,and a force analysis of an 8-cable driven parallel manipulator.To obtain end-force output in a low-gravity environment,the cable force has to be controlled to counteract gravity.In addition,a force-position mix control strategy is proposed to proactively control the cable force according to the force optimal distribution given by the closed-form force distribution method.Furthermore,a suitable choice for an end-force output is obtained by modeling the effect of cable force on end-force output.Experimental results show that the actual cable force agrees well with the calculated force distribution,indicating that it is feasible to realize end-force output in a low gravity environment.
基金supported by National Natural Science Foundation of China(No.52105502)Fund of National Engineering and Research Center for Commercial Aircraft Manufacturing(Nos.COMAC-SFGS-2019-263 and COMAC-SFGS-2019-3731)the Fundamental Research Funds for the Central Universities(No.3042021601).
文摘This study proposed a force and shape collaborative control method that combined method of influence coefficients(MIC)and the elitist nondominated sorting genetic algorithm(NSGA-II)to reduce the shape deviation caused by manufacturing errors,gravity deformation,and fixturing errors and improve the shape accuracy of the assembled large composite fuselage panel.This study used a multi-point flexible assembly system driven by hexapod parallel robots.The proposed method simultaneously considers the shape deviation and assembly load of the panel.First,a multi-point flexible assembly system driven by hexapod parallel robots was introduced,with the relevant variables defined in the control process.In addition,the corresponding mathematical model was constructed.Subsequently,MIC was used to establish the prediction models between the displacements of actuators and displacements of panel shape control points,deformation loads applied by the actuators.Following the modeling,the shape deviation of the panel and the assembly load were used as the optimization objectives,and the displacements of actuators were optimized using NSGA-II.Finally,a typical composite fuselage panel case study was considered to demonstrate the effectiveness of the proposed method.
